Call-distributing telephone system.



J. H. LEVI'S, JR.

CALL DISTRIBUTING TELEPHONE SYSTENI. APPLICATION FILED ocnzs. 1915.

1293,81 "7. Patented Feb. 11, 1919.

g I 3 SHEETSSHEET 1.

Q L 3 Wiirwsses f7Z06727f0f (E7171 HZ/evw, (fr? J. H. LEVIS, in.

CALL DISTRIBUTING TELEPHONE SYSTEM.

APPLICATION FILED ocT. 25. I9Ifi.

1,293,817. Patented Feb.11,1919.

I I I (O 1) Ji w x I? I In 1 I I? I I g Y I. g j 1 5 I I g I I I I I q @NQ@\OR% Q Ii $8 I Q g Q $1 *8 KO h g a messes: frwe/ztofi (707m HLeuz'sxfh XMW fig WM ridzwzw J. H. LEVIS, JR.

.CALL DISTRIBUTING TELEPHONE SYSTEM.

APPLICATION FILED ocr. 2 5. 191s.

Patented Feb. 11, 1919.

3 SHEETS-SHEET 3 7mm fiygm w w -m Attorneys .tion of similar problems.

JOHN H. LEVIS, JR., OF ROCHESTER, NEW YORK,' ASSIGNOR TO STROMBERG-GARLSON TELEPHONE MANUFACTURING COMPANY, OF ROCHESTER, NEW YORK, A. CORPO- RATION OF NEW YORK.

CALL-DISTRIBUTING TELEPHONE SYSTEM.

Specification of Letters Patent.

Q Patented Feb. 11, 1919.

Application filed October 25, 1916. Serial No. 127,520.

To all whom it may concern Be it known that I, JOHN H. LEVIS, Jr., a citizen of the United States, residing at Rochester, in the county of Monroe and State of New York, have invented a certain new and useful Improvement in Call-Distributing Telephone Systems, of which the following is a full, clear, concise, and exact description, reference being had to the accompanying drawings, forming a part of this specification.

The present invention provides an improved call-distributing telephone system.

The advantages of general call-distribution are well recognized by those skilled in the art. The total number of terminals is less; there is a general gain in speed in reaching an idle operator; the load on the operators is more easily distributed, and the wear on the apparatus is equalized. Numerous other advantages accrue.

However, complications often arise which make it diflicult to employ the full advantages of call-distribution, due to other factors entering into the problem, necessitating an entirely different solution. The definite problem which I have been enabled to overcome is the following: 3

There is a central, or main, exchange G, and an outlying or branch exchange B. A number of the subscribers at the B ex.- change enter a large percentage of calls for the C exchange, but also enter calls for the local or B exchange. Others of the subscribers at the B exchange enter local calls almost exclusively. The subscribers who call the central exchange ordinarily want prompt service to that point, because the majority of their calls go there and they would be less afiected by slightly slower service in calling local or B exchange subscribers. The other B exchange subscribers are more interested in obtaining prompt service on their local calls and they would be less affected by slightly slower service on their central exchange calls.

The object of the present invention is the provision of a system which will satisfy the above contradictory requirements and which will also provide means for the solu- Other more specific objects will be apparent from the following description.

I provide the first class of subscribers, namely the central exchange, with individual switches that allow them to select automatically an idle trunk leading to the central exchange. The trunks connecting the two exchanges terminate at the central exchange preferably before a number of operators positions at'the central exchange.

I also provide'these lines of the first class with multiple jacks at the B exchange, so that calling lines of the second class terminating in the B exchange or trunk calling lines fromthe central exchange may be connected with these lines as called lines, in the well-known manner.

To take care of the calls by this first class of subscribers, or other subscribers either of the first or the second class having terminals in the B exchange, I provide a special revertingposition having jacks connectible with each of the trunks used in automatic trunking to the central exchange. An automatically-distributed call appears on one of the positions at the C exchange, and if it is for a line having terminals in the B exchange, the C operator who answered thecall communicates with the reverting call operator over an order wire, deslgnating to the revertin call operator the trunk upon.

which the call appeared. The reverting call operator then completes the connection in the B exchange in any preferred or wellknown manner.

For the second class of subscribers, which may constitute the greater portion of the total number of subscribers at the B ex-.

between the two exchanges, are automatically distributed to terminals at the central exchange. i

In the accompanying drawings compris- Y matically-zby the lines A-B. The line A is connected bymeans of an automatic switch S tohave access to a number of trunks leading to the central exchange. The other class ofsubscribers-linestypified by the line-B terminates in'the branch exchange in the usual line acks and has multiple terminals, .as is well-wknownto those-skilled in the art, the 'samewnot being-illustrated in this dia- -gram,- forthe sake-ofclearness.

=The subscriber connected by the line B calls an operator at the'branch exchange and obtains connection in the well-known manner, by means of anoperatofis cord circuit and multiple terminals of-the called 3 line. ln-case the called party desired by the .B subscriber has line terminals inthe central exchange, the operator at the branch exchange will connect the B subscriber "through a'trunk line to'the'main exchange, 5 where a main-exchange operator connects the trunkwith the desired called line,'as is wellfunderstood in the art.

lllhe Asubscriber s,sub-station is provided "with theusual transmitter 1, receiver 2, hookswitch 8,'a-nd calling'signal 4, connected by means of the line-wires 5 and 6 to vthesprin'g tQI'mlllEtlS 7 =-and 8 of-the cut-off relay CU, having-windings 9 and 10. 'When the A subscriber. takes the receiver '2 oft the switch 5 hook to close the bridge across the lines 5 and 6, .current;:flows from the battery Q which is a common batterylocated at centralyover the bus 13, wire 12, motor-relay MR, wire 11,,back contact of'thespring'S,

line-wire 5, through the apparatus at the substation A, back over line-wire 6,a-rma- 'ture-spring 7,1-and back contact 1 to ground at G This energizes the. motor-relay 'MR whichattracts its armatures 1 1 and 15 and 16-to='close the'circuit throughthe interrupter 1 for 'the motor-magnet MM, to cause: theselecting-swit-ch 'S to connect the calling'line with an idle; trunk leading to the main exchange. The circuitfor the motor-magnet may be traced .as follows: grounded battery 'Q,'bus .l3, pilotirelay 17, wireQtS,throughthe interrupterl, the motor-magnet MM,uwire= 19, frontcontact and armature spring 16, wire 20, back contact Gian-d 'aa'rmatu-rc tsprlng 101:: the cut-1n.

relay CI, wire 22, armature 15, and front contact thereof to ground at G The lnterruptions of current through the motor-magnet. cause the switch-arms 23,2 1 and 25 to fore the switch-arms or wipers, '23, 2 1 and 25 arestepped onto the next contact. 7

The switch S comprises three wiping 'contacts'31, 32,-which are in connection with the extension of the line limbs 6 and 5,respectively, and the contactf33,-which is connected to the private wire 34. The contacts 35,

86 and 37; are-grouped about the stationary contacts 31, 32 and 33ssothat as the switch- --ar1'ns 23, 21 and are steppedsforward the line-limbs 6 and5-of'the.private wire 3 1 will .be brought successively 3111130 "contact 'with the trunks and Y their corresponding tl111fl wires, successively.

Assuming that the .trunk having the 1 transmission-strands 38 an'd89 and the third wire 10 is not engaged, and that thesw-itclr arms step forward to place the segments 31, 32 and 33 in contact with thetransmission- --strands and thethirdwvire of this trunk, respectively, the busy-test: circuit throughathe c'ontact'80 and the cut-in relay C1 will be formed as follows: from ground at G' through the wire 41, contact S0, wire 42, through the front contact of the armatures )ring14;,--wire 13, through the one winding 1 1 of the cutin' relay CI, through thewire 34500 the segment 33, overone of the switcharms to the terminal 37- =.and third wire 40 of the trtmk (continued o11 .seco11d' -sheet), through the. armature- 17 iofithe cut-off relay a6; back contacts of this arinature, wire -418, armature-contacte9 of the release-retard r'elay 50, backcontacts' oftherarmature, wire :53, through the service-jack 54:,which is normally closed by;means of a' short-circuitedservice plug ooithrough-the wire 56, relay 57, release-retard contact breaker 58,

and to groundedobattery Q over the -bus-bar 'The release-retard: circuittbreaker RR,

shown 'atithe lower right-hand cor-nerof Sheet 2, comprises .acommutator' 59 :and a brush :60, :arranged to break the circuit through the, eomn'r'utator. and brush only for an. instant: at the end of each three-second perloctofitime.

' Theabovecircuit being completed through the winding 44 0f the cut-in relayUi energizes said relay to connectthei 11116-11111b extensions o and 6 through the front contacts of the armaturcs 61 and 62 to the terminals 31 and 32 in the switch, and thereby to the limbs 38 and 39 of the trunk which has been selected.

Attraction of the armature 21 of the relay CI closes a holding circuit for this relay and a pull up circuit for the relay CU as follows: grounded battery Q, bus-bar 13, wire 12, through the winding 10 of the cutoff relay CO, winding 45 of the cut-in relay CI, front contact of the armature 21, wire 22, armature of the motor-relay MR, through the front contact thereof to ground at G it being noted that the motor-relay MB is still held closed by the current passing out over the line-limbs 5 and 6. The current for the motor-magnet is broken upon the first energization of the relay CT at the armature-contact 21. Hence, movement of the switch is prevented after an idle trunk has been found.

The energization of the cut-off relay CO and the cut-in relay CT now places the substation A in direct circuit with the limbs of the selected trunk, 38 and 39. The opera tion of the cut-off relay G0 has removed the ground G from the wire 22 by opening the circuit of the motor-relay at the armature contact 8.

The relay 57, which is in the circuit of the release-retard 58, controls in common with the transmission-relay 63 a pair of armatures 64 and 65. When the armatures 64' and 65 are attracted, there is placed a ground upon the third wire 40 of the trunk, so as to maintain a circuit for the windings 10 and 45 on the relays CO and CI, respectively. This circuit may be traced as follows from ground at G: wire 66, armature 65, front contact thereof, wire 40, bank contact 37 of the third wire, switch-wiper, switch-segment 33, wire 34, wire 67, armature 68 of the relay CO, front contact thereof, wire 69 to the armature 15, and from there to the wire 22, which is connected to the armature 21 through the front contact of the armature 21 of the cut-in relay GI, winding 45 of said relay, through the winding 10 of the relay CO, and to battery over the wire 12 and the bus 13. This circuit serves to hold the relays CO and CI energized and at the same time places ground upon the third wire 40, so that multiple terminals appearing in other switch-banks will not be selected by other calling lines.

Simultaneously with the formation of the above circuit, the transmission-relays 63 and 64, through which battery is fed to the calling line, are energized, so that even if the relay 57 has its circuit broken at the end of a three-second period by the release-retard 58, the ground upon the third wire 40 will be maintained by the energized condition of the battery transmission-relay 63. The circuit for battery to the calling line may be traced as follows: battery Q, bus-bar 13, Wire 70, transmission-relay '63, wire 71, which is connected to the talking-strand 39, through the switch bank contact 36, switchwiper and switch segment 32, to the callingline extension 5', over the calling line, through the switch-hook at the sub-station, through the side 6 of the calling line, lineextension 6, switch segment 31, switch-contact 35, talking-strand 38, wire 72, ground transmission relay 64, and ground at G.

The two sides of the trunk- 38 and 39 are connected together through a repeating coil having the halves of its winding 74 sepa rated by a condenser 75. The complementary halves of the adjacent winding of the repeating coil 76 are normally open at the front contacts of the armature 77 of the transmission relay 64. When the relay 64 is energized as above described, the repeat ing coil 76 will be closed at the armature 7 7, so that voice current Will be repeated from the trunk strands 38 and 39 to the corresponding trunk strands 78 and 79, or the reverse. The trunk strands 78 and 79 are broken through the armature-contacts 80 and 81 of the cut-0E relay 46, which becomes energized when the reverting-call operator, located at the reverting-call position, inserts the plug of a connecting cord in the jack 87 corresponding to the given trunk on the reverting-call position. The strand 78 is connected to ground at G through the back armature lcontact- 82 of the cut-off" relay 83, which is located at the main exchange. The strand 79 is connected by way of the back contact of the armature 84 through a signaling-relay 85 to battery Q by way of the battery-bus 13. Thus, as soon as the transmission relay 64 closes the two sides of the talking trunks 78 and 79 together at the contact 77, a current will flow from the battery Q through the signaling relay 85 over the trunk strand 7 9, through the windings of the repeating coil 76, which have been closed at the contact 77, back to ground over the trunk strand 78. The calling signal L, which may be a small incandescent lamp, or the like, is displayed in such position as to notify one of the opera tors at the main exchange that the particular trunk ending in the jack J has been selected by a calling line. An operator at the main exchange answers the call by in.- serting the plug P of one of her cord pairs into the jack J, thus operating the cut-off relay 83 and placing her set, which is bridged across the cord strand at this time, in communication with the calling subscriber at the sub-station A.

Assuming that the call initiated by the subscriber A is for a subscribers line having terminals in the main exchange, the main-exchange operator will then complete the call, as through .the line leading to the sub-station D, in the well-known manner.

Assuming that the calling subscriber at the sub-station A desires connection with a subscriber having a line terminating in the B exchange, the operator answering the call at the main exchange upon being notified the calling party at A that he desires a local or B exchange connection, will notify the reverting-call operator at the B exchange, as by means of the order wire 86, which has been shown diagrammatically as connecting the main exchange with the B exchange re verting-call operators yposition, notifying the reverting-call operator that the calling 7 subscriber on the trunks 7 8-7 9 desires a local or B exchange connection. The reverting-call operator plugs into the revertingcallrjack 87, operating the cut-off relay 4:6,

which, through the armature contacts 80 and 81, and the front contacts connected thereto, places her telephone set in communication with the subscriber at A. Upon ascertaining the number of the called subscribers line, the reverting-call operator makes connection through multiple jacks, a complete set of which is available to her, to the line of the desired subscriber.

Each of the subscribers lines leading into the B exchange is provided with multiple jacks, whether the line is provided with line signaling apparatus terminating in the B exchange, or with aselecting-switch, through trunks and line-signaling apparatus at the main exchange; and if the party at the sub station A calls for connection with a similar line, which is connected to an automatic switch, connection will be made through the multipl jacks, as illustrated at M, to the de sired called subscribers line.

When the cord circuit C is connected to the multiple jacks M, battery flows over the tip-strand of the cord circuit, tip spring 88 of the jacks M, through the armature 62, back contacts thereof, wire 100, winding 9 of thecut-ofi' relay GO, to ground at G This operates the cut-off relay CO to disconnect the automatic switching mechanism, holding the line open at the armaturecontacts 61 and 62 to the deenergization of the cut-in relay CI. 'l Vhen the operator at the main exchange has inserted the plug P in the jack J, the answering supervisory signal 101 will be subject to the open or closed condition of the line at the switch-hook 3.

As soon as the calling subscriber places the broken.

switch-hook 3 is not followed immediately. by release of the switch S and the connected apparatus. The switch S is of the non-normaling typethat is, it rests indilferently instantaneous release of the apparatus upon 7 a short or accidental opening of the switchhook contact, that I have provided lease-retard before mentioned.

The release-retard may allow theconnection to be broken within any time less than three seconds after the main circuit is Inasmuch as the relay 57 first places busy potential upon the private wiper 33 through the contact 64, this relay, which forms a:looking circuit for itself, is con nected through the release-retard 58p If after having obtained connection with an idle trunk, as 38-39, the subscriber atA abandons the call, the busy potential will the rebe taken off the private wiper 33 as soon as from the relay 5? to these relays 63 and 64, and the breaking of the busy potential for the private segment 33 in the. switch S is thereafter placed upon the relay 50. *The circuit of the relay 50 may be traced as follows: grounded battery Q, busbar 13, wire 89, winding 52'of the relay 50, wire 90, front contact of the armature 91 of the transmission-relay 64, wire 92, armature-contact 64 and to ground by way of the wire 66 at G This groundat G is also in connection with the private segment 33 by way of the armature 65 and the private wireor third wire-lt() ofthe trunk-switches connected to the switch. This circuit through the winding 52 is broken, however, as soon asthe' calling subscriber breaks his line-circuit at the switchhook 3, either by accident or uponthe conclusion of the conversation; It is desirable that the busy potential should continue for a short time thereafter, so that in case .of accident restoration of the switchhook would allow a subscriber at A to continue with his conversation. Energization of the relay 50 attracts the armatures 49'and 9 3, the armature 49 breaking the circuit through relays?! and connecting the third wire 40 to ground at G through the wire 94 and the front contact of the armature 49.

A locking circuit for the winding 51 is formed through the armature 93 from ground G through the release-retard circuit-breaker RR to the grounded battery Q. Hence, after the subscriber at A places his receiver on the switch-hook, ground from the wire 94 and ground G will be maintained upon the private wire 40, even though the Winding 52 be deenergized, until the locking circuit through the winding 51 is broken at the release-retard commutator RR.

If connection is made through the reverting-call jack 87 to the trunk-strands 7 8 and 7 9, the energization of cut-off relay 46 will attract its armature 47 and place ground through wire 94 and ground G upon the third wire 40, and thus maintain a busy potential upon the private segment 33, so long as the operators cord circuit is connected to the reverting-call jack, the connection being cut off from the release-retard by the armature 47 being attracted to its front contact. Hence, so long as the plug'is in the jack 87, the trunks 38 and 39 cannot be selected by another calling switch, such as S, nor is the line circuit to the sub-station A broken, so that the line A could be called by some other calling subscriber. This is to prevent any possibility of a connection being made at the reverting-call operators position without the knowledge or control of the connected subscriber.

It will be noticed that in the service-jacks and service-plugs I have provided switching means for cutting any desired trunk out of service, such as may be desirable when all of the calls are to be switched to a given position, in the night or during periods of very light load. Removal of the service-plug cuts off the battery connection to the wire 40,'so that there is no potential for stopping the switch S when the contacts thereof wipe over the stationary contacts of the corresponding trunk. This switching mechanism is also useful in preventing connection of a calling line with a trunk which is out of order or under repair, or the like.

The system which I have illustrated is provided with pilot means common to the exchange for indicating an abnormal condition of any one of the line-switches, and I have also provided means individual to each trunk to indicate trouble or incorrect operation on the calling line connected to the trunk. The interrupter pilot-relay 17 controls an interrupter pilot-lamp 96 and an audible signal 97 for apprising the attendants that one of the switches is constantly rotating. The pilot-relay 17 is provided with means for preventing the same from becoming energized upon a short period of interrupted current-flow therethrough, so that only when interrupted current has been flowing through this relay for a considerable time, the circuit of the interrupter pilotlamp 96 and the audible signal 97 will be closed.

I have also provided means for indicating ground on either side of a calling subscribers line.

Assume that a ground is placed upon the sleeve side 5 of the calling subscribers line, as indicated by the dotted line, and a ground at G on Sheet 1. As soon as connection is established with an idle trunk, such as the ones illustrated in the drawings, 38 and 39, the transmission-relay 64 will not be energized, due to the fact that it is short-circuited by the ground at G. As a consequence, the switch S will not release and the red lamp 98 will remain energized continuously, the transmission relay 63 holding ground G upon the third wire 40 to maintain the switch S in busy position, and holding the cut-ofl' relay CO and the cut-in relay CI in energized condition. The green lamp 99, which is preferably placed in the wirechiefs desk, will also be permanently displayed, due to the circuit closed through it and the ground at G Thetransmission-relay 63 holds the armature 65 in the attracted position, but the release-retard relay 57 periodically drops the armature 64, thereby causing flashing of the red and the green lamps intermittently.

The operation of the system may briefly be described as follows:

Assuming that the subscriber at A is provided with a line having a selecting-switch, such as the switch S, and that he desires connection with a subscribers line having terminals in the main exchange. The A subscriber raises the receiver from the switchhook, closing a circuit through the motorrelay, causing the automatic switch S to step forward to find an idle trunk circuit. An idle trunk circuit will be selected, because of the battery potential upon its private wire 40, which will energize the cut-in relay CT and open the motor-magnet circuit. At the same time a holding circuit for the relay CI and a pull-up circuit for thecut-01f relay CO is formed. This circuit, which is first closed through the ground G controlled by the motor-relay MB, is transferred to the ground G by means of the release-retard relay 57. The ground is thereafter maintained by the transmission-relay 63, which remains energized as long as battery is fed out over the calling line.

The transmission-relay 64 closes the linelimbs 78 and 7 9 through the repeating coil and causes the line-signal to be displayed at the main exchange. If the call is for a subscriber having terminals in the main exchange, the main-exchange operator connects the A operator with the called partys line, which in this case we will suppose to be the subscribers line D, and conversation 'is carried on and completed 1n the usual manner. Upon restormg the receiver to the switchhook at the sub-station A, the transmissionrelay '63 is denergized but release of the ground potential from the private segment 33 is not accomplished until the relay is deenergized by breaking of the circuit through the winding 51 by the release-retard circuitbreaker. Thereupon busy potential is re moved from the private segment 33 in the switch and the cut-in and cut-ofl' relays are denergized, restoring the parts to normal.

If the call initiated by the A subscriber should be for a subscriber whose line terminated in the B exchange, the main-exchange operator would refer the call to the revertingcall operator, apprising her of the trunk on which the call appeared over the order wire. Thereupon the revertingcall operator would connect the trunk with the line of the desired subscriber, such, for instance as a subscriber B, having line terminals in the B exchange. Busy potential is held on the private segment 33 and the calling line is locked to the trunk selected until the reverting-call operator withdraws the plug from the corresponding jack.

While I have described my invention with reference to the details of a particular embodiment, it is to be understood that the invention may be practised in other forms of apparatus and with various modifications and substitutions which will at once be apparent to those skilled in the art. I consider such changes to come within the spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is the following:

1. In combination, a plurality of sub scribers lines terminating in a branch exchange, a plurality of subscribers lines terminating in a main exchange, multiple jacks connected to all of said subscribers lines and located in the respective exchanges, one class of said branch-exchange subscribers lines having active automatic switches connected thereto, said switches being invariably actuated upon initiation of calls originating on said one class of subscrlbers lines, trunks between the branch and the mam exchange 7 having manual switching terminals in the 'when'calling to said main exchange and for interconnecting all of said subscribers at said branch-exchange,

2. In combina tion, a branch exchange,

subscribers lines terminating therein, a mam exchange, subscrlbers lines terminating in said mam exchange, trunks extendlng between and having operator-controlled 'swltching terminals at said main exchange,

automatic switches at said branch exchange, a part of said branch-exchange subscribers lines having control over said switches to connect said subscriberslines when calling with idle ones of said trunk'lines, line signals for said trunks at said main exchange, others under the individual control of certain ones of said branch-exchange subscribers lines for causing said switches to connect the subscribers line with idle ones of said trunks, line signals for said trunks at said mainexchange, others of said branchexchange subscribers" lines having line signals at said branch exchange, multiple ter minals for all of said branch-exchange subscribers lines at the branch-exchange and means for interconnecting said branch-exchange subscribers lines at said branch exchange. 7

4, In combination, a main exchange, a branch exchange, lines terminating in each of said-exchanges, a plurality of trunks connecting said exchanges, line signals and operator-controlled switching terminals for said trunks atsaid main exchange, said branch-exchange lines having multiple terminals in said branch exchange, a plurality of said branch'exchange lines having subscriber-controlled automatic selecting means for selecting an idle one of said trunks when calling, a reverting-call operators position at said branch exchange, and operator-con trolled switching terminals at said position for interconnecting, said trunk lines with e 7 controlled switching terminals for said 7 trunks at said main exchange, said branchexchange' lines' having multiple terminals in said branch exchange, 'a plurality of said branch-exchange lines having automatic sei lecting means for selecting an idle one of said trunks when calling, and displaying a calling signal at the main exchange, a reverting-call operators position at said branch exchange, and operator-controlled switching terminals for said trunks at said position, said switching terminals having means for elfacing the line signal at the main exchange.

6. In combination, a main exchange, a branch exchange, subscribers lines terminating in said exchanges, a plurality of trunks connecting said exchanges, line signals and operator-controlled switching terminals for said trunks at said central exchange, said branch-exchange lines having multiple terminals in said branch exchange, a plurality of said branch-exchange lines having automatic selecting means for selecting an idle one of said trunks and displaying a calling signal at said main exchange when calling, a reverting-call operators position at said branch exchange, and operator-controlled switching terminals at said position for connecting a selected trunk with any one of the branch-exchange subscribers lines, said switching terminals having means for breaking the trunk circuit to the central exchange and for efiacing the line signal thereat.

7 In combination, a main exchange, a branch exchange, subscribers lines terminating in each of said exchanges, trunk lines connecting said branch exchange with said main exchange, automatic switches at said branch exchange, said switches operable to connect calling subscribers lines at the branch exchange to an idle one of said trunk lines leading to the main exchange, means under the control of a part of the subscribers at said branch exchange for causing said automatic switch to connect said subscribers lines with an idle trunk, means for placing a busy potential upon the terminals of saidtrunks when selected, a reverting-call operators position at said branch exchange, switching means under the control of the operator at said position for connecting said trunks with subscribers lines having terminals in said branch exchange, said operator-controlled switching means having means for maintaining a busy potential upon said trunk terminals after the subscribers line connected to said trunk has been disconnected at the sub-station.

8. In combination, a subscribers line, an automatic switch individual thereto having access to a plurality of trunk lines, said switch being under the control of subscribers switch-hook for selecting an idle one of said trunk lines, means for placing a busy potential upon the private wire or said trunk line, said means comprising a battery transmission-relay, and means to retain said potential'up'on said wire, said last means comprising a relay, and means for periodically interrupting the circuit of said relay.

9. In combination, a subscribers line, a selecting switch individual thereto, means under the control of the subscribers switchhook for causing said switch to select an idle trunk circuit, a plurality of trunk circuits having contacts selectable by said switch, means for stopping said switch upon an idle trunk line, said means applying a busy potential to one of the terminals of said trunk line, said potential-applying means comprising a battery transmissionrelay connected to said trunk line, and means for retaining said busy potential upon the terminals of said trunk, said means comprising a periodically-operating circuitchanger.

10. In combination, an automatic switch, a plurality of lines selectable by said switch, said lines comprising a talking strand and a private wire, means for placing a busy potential upon the private wire of a selected switch, said means comprising a periodically-interrupted source of potential, a battery transmission-relay connected to said switch, and means under the control of said transmission-relay for supplying a constant source of potential to said third wire.

11. In combination, an automatic selecting switch, trunks having terminals selectable by said switch, said trunks comprising talking strands and a third wire, means operated by potential applied to the third wire of one of said trunks for stopping said switch in connection therewith, means for applying potential to said third wire, said means comprising a periodically-interrupted source of current, and a transmission-relay operated after the said switch is stopped upon the terminals of the corresponding trunks for applying a constant source of potential to said third wire.

12. In combination, an automatic selecting switch, a plurality of trunks having terminals selectable by said switch, said. trunks comprising a talking strand and a third wire, means underthe control of the subscribers switch-hook for starting said switch to connect the corresponding subscribers line with an idle one of said trunks, means for stopping said switch in contact with an idle trunk, said means comprising a source of periodically-interrupted current,

means for applying a constant potential to said third wire, said means comprising a transmissionrelay connected to the corresponding trunks, operator-controlled switching means connectible to said trunks, said switching means having means for applying a constant source of potential to said third WIIG.

13; In combination, an automatic switch, a plurality of trunk'lines selectable by said V adapted to apply busy potential tothe test t5 V V further means being periodically rendered switch, means under the control of the subscribers switch-hook for causing said switch to select an idle one of said trunks, said trunks comprising a talking strand and a third wire, means for applying a source of interrupted current to said third wire to render said trunks busy, operator-cont-rolled switching means at the terminals of said trunks for connecting the trunks with another subscribers line, and means interme diate the ends of said trunks for connecting said trunks to a subscribers line, said lastnamed switching means comprising means for applying a constant source of potential to said third wire to render the same busy.

1 In combination, a plurality of telephone lines, a plurality of line extensions, automatic switches for automatically interconnecting said lines and said extensions, each switch comprising testing contact-s, means controlled by the subscribers switch hook for causing the switch to connectthe telephone line with an idle extension, a battery transmission relay having means adaptedto hold the switch in closed position and for applying busy potential to the testing contacts, and further means for holding the switch in closed position and for applying lousy potential to the testing contacts, said further means being periodically ren-V dei'ed inactive.

15. In combination, a plurality of telephone lines, a" plurality of line extensions, automatic switches for automatically interconnecting said linesand said, line extensions, means controlled at the'subscribers station for causing the switch to connect the telephoneline with an idle line extension, a battery transmission relay having means adapted to hold the switch in closed position and further means for holding the switch in closed position, said further means being periodically rendered inactive.

16. In combination, a plurality of telephone lines, a'plurality of line extensions,- automatic switches for automatically interconnecting said lines .and said line extensions, each switch comprising testing con-V 'tacts, means controlled at the subscribens station for causing the switch to" connect the telephone llIie'Wltll an idle line extension, a battery transmission relay having means ing contact and further means for applying busy potential to the testing contact, said inactive. I

17. In combination a luralit of lines a a P y a plurality of line extensions, automatic switches for interconnecting the lines and the line extensions, a battery teed. relay on a the battery sideand a battery feed relay en 7 theVground side oftieextensions, a test contact in the switch, a holdinglrelay intermittently denergized, said relaybeing adapted trunk lines from the branch exchange termi nating and having call indicating apparatusat the main exchange, automatic switches associated with the trunk lines, said subscribers lines being divided into two'classes, the first class of lines having access forcalls originating on said lines to said automatic switches, the second class of subscribers 1 lines having no access to said SWllZCl'IBS,

means connectible to said trunk lines for diverting local calls arising on said first class of lines to the branch exchange and means for simultaneously eii'acingithe indicationof the call indicating apparatus of the corresponding trunk lines at the central station. V V

19. In combinatioin'a branch exchan main exchange, a plurality of subscribers lines having terminals at the branch ex-.

change for local interconnections, apluraL' ity of trunk lines from the branch exchange terminating in andhaving call indicating apparatus at the main exchange, automatic switches associated with the trunk lines, said subscribers lines being I divided into two classes, the first class of lines having access for ori 'inatin calls to said automatic switches only, local interconnectingmeans independent of SitltlitllilOlnttillC swltchesfor interconnecting the branch exchange terminals oi all of said subscribers, the second class of subscribers"lineshav ngno access to said automatic switches and means connectible to said trunk, lines 1 for V diverting; local calls arising on said'firstclassof 111163 to the branch exchange for connection with said local interconnecting means V 7 20. .In combination, a branch exchange, a

main exchange, a plurality of subscribers lines having terminalsia-t the branch exterminating in and having call indicating apparatus at the main exchange, V automatic switches associated with the trunk lines,-said subscribers" lines being divided into 7. two

classes, the first class of lines having access for originating calls to said "automatic V change for local interconnections,-

plural; ity of trunk lines from: the branch exchange switches only, local interconnecting means independent of said automatic switches for,

interconnecting the branch exchange termi- V nals of allot said subscribers, the second class. of subscribers lincshavingfno accssf '7 to said automat cswitches incans-connectgV V ible to aid trunk lines for diverting local i'sef calls arising on said first class of lines to the branch exchange for connection with said local interconnecting means, and means for simultaneously efiacing the indication of the call indicating apparatus of corresponding trunk lines at the central station;

21. In combination, a main exchange, a branch exchange, a plurality of subscribers lines terminating in the branch exchange, trunk lines leading from the branch exchange to the main exchange, said branch exchange having an operators position having regular line terminals for a plurality of said subscribers and having a reverting call operators position, automatic switches associated with the trunk lines and certain ones of said subscribers lines, and adapted to invariably connect said latter subscribers lines when calling, with the said trunk lines.

22. In combination, a main exchange, a branch exchange, a plurality of subscribers lines having interconnecting terminals in the branch exchange, trunk lines leading from the branch exchange to the main exchange, said branch exchange having an operators position having regular line terminals for a plurality of said subscribers and having a reverting call operators position, automatic switches associated with the trunk lines and certain ones of said subscribers lines and adapted to invariably connect said latter subscribers lines when calling with the trunk lines, said reverting call operators position having switching r terminals connectible to the trunk lines.

23. In combination, a main exchange, a branch exchange, a plurality of subscribers lines having interconnecting terminals in the branch exchange, trunk lines leading from the branch exchange to the main exchange, said branch exchange having an operators position having regular line terminals for a plurality of said subscribers and having a reverting call operators position, automatic switches associated with the trunk lines and certain ones of said subscribers lines and adapted to invariably connect said latter subscribers lines when calling with the trunk lines, said reverting call operators position having switching terminals connectible to the trunk lines, and having means for disabling the end of the trunk line terminating in the main exchange.

24. In combination, a main exchange, a branch exchange, subscribers lines having local interconnecting terminals at said branch exchange, said lines being of two classes, trunk lines between the branch exchange and the main exchange, automatic switches for invariably connecting a calling line of the first class to an idle one of said trunk lines for terminating a call of a subscribers line of the first class at the main exchange, local interconnecting means independent of said automatic switches having access to all of said local interconnecting terminals and means for the other class of lines for invariably terminating a call originating on a line of said latter class at the branch exchange.

In combination, amain exchange, a branch exchange, subscribers lines having local interconnecting terminals at said branch exchange, said lines being of two classes, trunk lines between the branch exchange and the main exchange, automatic switches for invariably connecting the calling lines of the first class to an idle one of said trunk lines for terminating a call of a subscribers line of the first class at the main exchange, local interconnecting means independent of said automatic switches having access to all of said local interconnecting terminals and means for the other class of lines for invariably terminating a call originating on a line of said latter class at the branch exchange, and reverting call interconnecting terminals at the branch exchange associated with the trunk lines for making connections between said trunk lines and a subscribers line of either class.

26. In combination, a main exchange having an operators position, a branch exchange having an operators position, subscribers lines having multiples in the branch exchange, one class of said lines having call-indicating apparatus at said branch exchange operators position, another class having no local call-indicating apparatus, trunks leading from the branch exchange to the main exchange, automatic switches for interconnecting calling lines of said latter class with idle trunks, and call-indicating apparatus associated with the trunks at the main operators position, a reverting call operators position at the branch exchange and an order wire from the main exchange operators position to the reverting call operators position.

27. In combination, a main exchange having an operators position, a branch exchange having an operators position, subscribers lines having multiples in the branch exchange, one class of said lines having callindicating apparatus at said branch exchange operators position, another class having no local call-indicating apparatus, trunks leading from the branch exchange to the main exchange, automatic switches for interconnecting calling lines of said latter class with idle trunks, and call-indicating apparatus associated with the trunks at the main operators position, a reverting call operators position at the branch exchange, an order wire from the main exchange operators position to the reverting call operators position, and switch means at the reverting call operators position for disabling the main exchange end of the trunks and for eflacing the indication of the corresponding call-indicating apparatus.

28. In combination, a main exchange, a branch exchange, subscribers lines of two classes, trunks from the branch exchange to the main exchange having automatic switches, means for automatically extending a call of a line of the first class invariably to the main exchange over one of said trunks, reverting call terminals at the branch exchange associated with the trunks between said automatic switches and the main exchange for making local interconnections between a calling line of the first class with another line of either class.

29. In combination, a main exchange, a branch exchange, subscribers lines of two classes, trunks from the branch exchange to the main exchange having automatic switches, means for automatically extending a call of a line of the first class invariably to the main exchange over one of said trunks, reverting call terminals at the branch exchange associated-with the trunks between said automatic switches and the main exchange for making local interconnections between a' calling line of the first class with another line of either class, and means for invariably terminating calls ofa subscribers line of the second class at'the branch exchange.

In witness whereof I hereunto subscribe my name this 14th day of October, A. D. 1916.

JOHN H. LEvIsJR.

Copies of this patent may be 'obtained for five cents each, by addressing the Commissioner of Patents, 'Wuhlngtom-D. 0;" 

